Preparation of filler-metal weld rod by injection molding of powder

ABSTRACT

A filler-metal weld rod of a filler-metal composition is prepared by providing a mass of metallic powders, mixing the metallic powders with a temporary thermoplastic binder to form an injection-moldable mixture, and thereafter injection molding the injection-moldable mixture at an injection-molding temperature above the thermoplastic temperature of the thermoplastic binder to form an injection-molded rod. Any excess thermoplastic binder is removed from the injection-molded rod, and the injection-molded rod is thereafter sintered to form a filler-metal weld rod, with the temporary thermoplastic binder removed in the step of sintering.

This invention relates to the preparation of filler-metal weld rod and,more particularly, to the preparation of weld rod of difficult-to-deformalloys.

SUMMARY OF THE INVENTION

In a form of welding, a metallic article to be welded is locally melted,and the melted metal is mixed with a second metal. The temperature isthereafter reduced so that the melted mixture solidifies. In oneapproach, the second metal is another article, so that the two articlesare joined together. In another approach, the second metal is an overlaydeposit that is also melted during the welding process, with the resultthat the first article is overlaid with the second metal.

A filler metal may be used in either of these approaches. In the joiningof two articles by welding, the filler metal may be added into themelted zone to fill the space between the two articles. In the overlayprocess, the filler metal may form substantially the entire overlay. Thefiller metal may be the same as one or both of the articles being joinedin the first approach. In the second approach, the filler metal may bethe same as the article being overlaid, such as when the dimensions ofthe article are being restored during a repair process, or of adifferent composition to provide particular properties to the surface ofthe overlaid article.

The filler metal is often supplied as a weld rod that is used inautomated welding apparatus and other welding procedures such as manualwelding. (As used herein, “rod” and “weld rod” include physical formsthat are considered rods and also physical forms that are consideredwires, avoiding the need for any arbitrarily selected distinction as towhether the physical form is a rod or a wire.) A heat source, such as anelectrical welding power supply or a beam source such as a laser orelectron beam, heats the region of the article to be melted, forming amolten pool. The filler-metal weld rod is gradually fed into the moltenpool to supply the desired volume of the filler metal.

The filler metal may be produced in rod form in various ways. In oneapproach, it is cast as a billet and then extruded or wire drawn tosmaller transverse size. In another approach, it is consolidated as apowder into a billet, and then extruded or wire drawn to smallertransverse size. In either of these fabrication techniques, the extrudedarticle is centerless ground to achieve the desired shape and size, andto remove the remnants of the extrusion operation. In other approaches,the rod may be cast to shape from powder or produced from a tube filledwith a powder mixture.

Some alloys of interest as filler metals in welding applications,notably titanium aluminides and nickel-base superalloys with a highvolume fraction of gamma prime phase when heat treated, cannot be wiredrawn due to their work hardening properties and limited ductilities.The welding filler metal weld rod is therefore conventionally producedby a specialized extrusion process, followed by acid etching andcenterless grinding of the extruded material. As a result, themanufacturing yields of usable weld rod are low, typically about 25percent of the weight of the starting material. The process is alsorelatively expensive. The cost of the weld rod is therefore high,relative to the material cost. More recently, techniques have beendeveloped to make the weld rod from powder by specialized casting orwire drawing of a powder-filled tube.

Although the recently developed processes for manufacturing titaniumaluminide and high-gamma prime nickel-base superalloys are operable,there continues to be a need for a further-improved approach to thefabrication of weld rod and related types of products. The presentinvention fulfills this need, and further provides related advantages.

BRIEF SUMMARY OF THE INVENTION

The present approach provides a method for producing filler-metal weldrod that is widely applicable. However, the process is mostadvantageously applied to weld rod wherein the filler metal is adifficult-to-work material such as a high-gamma prime nickel-basesuperalloy or a titanium aluminide, because there is no grossdeformation of the weld rod required during the manufacturing process.The present approach produces a weight yield of usable weld rod, ascompared with the weight of the starting material, of near 100 percent.There is excellent process economics and reduced cost of the weld rod.The quality of the weld rod is high, with low incidence of defects thatcan be transferred to the welded structure. New compositions may bereadily prepared by the present approach.

A method for preparing a filler-metal weld rod of a filler-metalcomposition comprises the steps of providing a mass of metallic powders,wherein the mass of metallic powders together have the filler-metalcomposition, and mixing the metallic powders with a temporarythermoplastic binder to form an injection-moldable mixture, preferablyat a mixing temperature above the thermoplastic temperature of thethermoplastic binder. The injection-moldable mixture is thereafterinjection molded at an injection-molding temperature above thethermoplastic temperature of the thermoplastic binder, to form aninjection-molded rod. Thereafter, excess thermoplastic binder is removedfrom an external surface of the injection-molded rod. It is preferredthat the process be performed without any added water present, in thethermoplastic binder or otherwise. The injection-molded rod isthereafter sintered, preferably by solid-state sintering, to form thefiller-metal weld rod. The temporary thermoplastic binder is removed inthe step of sintering. The filler-metal weld rod preferably has acylindrical diameter of from about 0.010 to about 0.250 inch, morepreferably from about 0.035 to about 0.070 inch. Optionally, thefiller-metal weld rod may be centerless ground after sintering orfurther densification treatment.

The metallic powders may be prealloyed and all of substantially the samecomposition. The metallic powders may instead be of differentcompositions, but selected so that their net composition is thefiller-metal composition. The prealloyed approach is preferred, so thatthe finished weld rod is macroscopically and microscopically uniformthroughout and already of the filler-metal composition throughout.Otherwise, some alloying is required during the processing or the use ofthe weld rod in a welding procedure, and there is a possibility ofincomplete alloying although full alloying occurs during the subsequentwelding operation. In any event, it is preferred that the metallicpowders are generally spherical with a diameter of not greater thanabout 400 micrometers.

The present approach does not require gross deformation of the weld rodat any stage of its fabrication. Consequently, it is most beneficiallyused to prepare weld rod of filler-metal compositions that are difficultto deform because of their high strengths, low ductilities, or otherproperties. One preferred filler metal is a nickel-base superalloy thatis heat treatable to produce more than about 30 volume percent gammaprime phase. Examples include Rene™ 142 alloy and Rene™ 195 alloy.Another preferred filler metal is an intermetallic alloy such as atitanium-base intermetallic alloy. An example is a composition a nominalfiller-metal composition in atomic percent of from about 45.5 to about48.0 percent aluminum and from about 48 to about 50.5 percent titanium,with the balance other elements.

The present approach is amenable to incorporating nonmetallic particlesinto the weld rod. In this approach, nonmetallic particles are mixedwith the metallic powders and with the thermoplastic binder prior toinjection molding.

The injection molding may be accomplished by any operable approach.Preferably, an injection-molding apparatus is provided. Theinjection-molding apparatus includes an injection head with an injectionnozzle, and a movable receiver positioned to receive theinjection-moldable mixture flowing from the injection nozzle. Theinjection-moldable mixture is loaded into the injection head. Theinjection-moldable mixture is forced out of the injection nozzle ontothe movable receiver, while moving the movable receiver away from theinjection nozzle at the same linear rate as the injection-moldablemixture is forced from the injection nozzle.

After the step of sintering, the filler-metal weld rod typically has arelative density of not greater than 90 percent. For many weldingapplications, this relative density of the filler-metal weld rod issatisfactory. If a higher relative density is desired, after sinteringthe filler-metal weld rod may be densified to greater than 90 percentrelative density by hot isostatic pressing.

The present approach provides a convenient and economical approach toproducing filler-metal weld rod. Filler-metal weld rod of anycomposition that is available in powder form may be made, even ofdifficult-to-draw metals such as high-gamma prime nickel-basesuperalloys and intermetallics. Compositional control of the weld rod ishighly precise. New compositions may be readily produced, without theextensive experimentation and process development required in most otherprocesses when making weld rod of a new composition. The oxygen contentof the final weld rod is below that expected from the oxygen contents ofthe starting materials, suggesting a chemical reaction and removal ofthe oxygen.

Other features and advantages of the present invention will be apparentfrom the following more detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings, whichillustrate, by way of example, the principles of the invention. Thescope of the invention is not, however, limited to this preferredembodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block flow diagram of an approach for practicing theinvention;

FIG. 2 is a schematic illustration of an injection-molding apparatus;and

FIG. 3 is an elevational view of a filler-metal weld rod produced by theapproach of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 depicts the steps in a method for preparing a filler-metal weldrod of a filler-metal composition. A mass of metallic powders isprovided, step 20. The mass of metallic powders taken together have thefiller-metal composition. The metallic powders are preferablyprealloyed. That is, each powder particle has the net filler-metalcomposition as to metallic elements. Prealloyed metallic powders forcompositions of interest are available commercially, or can be preparedspecially by known techniques. The metallic powder particles may insteadbe of different compositions, but selected so that the net compositionof all of the metallic powder particles taken together is thefiller-metal composition of interest.

The present approach is operable to produce any of a wide range offiller-metal compositions. As long as prealloyed powders or powders whocompositions can be combined to define a composition of interest areavailable, the present approach may be utilized. However, somefiller-metal weld-rod compositions are of particular interest, becausethey are difficult or impossible to produce by conventional techniques.One preferred filler metal is a nickel-base superalloy that is heattreatable to produce more than about 30 volume percent gamma primephase. Members of this class of materials work harden so rapidly and areof such limited ductility that it is difficult to produce them by wiredrawing or other technique requiring gross deformation of the materialto form the weld rod of this filler metal. Examples of such high-gammaprime nickel-base superalloys include Rene™ 142 alloy having a nominalfiller-metal composition in weight percent of about 12.0 percent cobalt,about 6.8 percent chromium, about 1.5 percent molybdenum, about 4.9percent tungsten, about 2.8 percent rhenium, about 6.35 percenttantalum, about 6.15 percent aluminum, about 1.5 percent hafnium, about0.12 percent carbon, about 0.015 percent boron, balance nickel and minorelements; and Rene™ 195 alloy having a nominal filler-metal compositionin weight percent of from about 7.4 to about 7.8 percent chromium, fromabout 5.3 to about 5.6 percent tantalum, from about 2.9 to about 3.3percent cobalt, from about 7.6 to about 8.0 percent aluminum, from about0.12 to about 0.18 percent hafnium, from about 0.5 to about 0.6 percentsilicon, from about 3.7 to about 4.0 percent tungsten, from about 1.5 toabout 1.8 percent rhenium, from about 0.01 to about 0.03 percent carbon,from about 0.01 to about 0.02 percent boron, balance nickel andincidental impurities.

Another preferred filler metal is an intermetallic alloy such as atitanium-base intermetallic alloy, which also has a high rate of workhardening and limited ductility, and therefore is difficult orimpossible to form into weld rods by gross deformation processes.Titanium aluminide is an example. One such class of titanium aluminidefiller-metal weld rods have a composition in atomic percent of fromabout 45.5 to about 48.0 percent aluminum and from about 48 to about50.5 percent titanium, with the balance other elements. Examples ofother intermetallic alloys of interest include nickel aluminide, niobiumsilicide, and molybdenum silicide.

Some other alloys of interest are difficult to manufacture as weld rodbecause of their high work hardening rates that make them difficult todraw at room temperature. The conventional approach to weld-rodfabrication for these materials requires multiple steps of cold drawingand annealing, so that the production cost is high. The present approachallows the production of such materials much more economically. Examplesinclude Waspalloy, having a nominal composition in weight percent of13.0 percent cobalt, 0.04 percent carbon, 1.5 percent aluminum, 3.0percent titanium, 19.0 percent chromium, 4.3 percent molybdenum, balancenickel; Ti-64, having a nominal composition in weight percent of 6percent aluminum, 4 percent vanadium, balance titanium; A286, having anominal composition in weight percent of 24-27 percent nickel, 13.5-16percent chromium, 1.9-2.35 percent titanium, 1.0-1.5 percent molybdenum,0.1-0.5 percent vanadium, 0.08 percent maximum carbon, 2.0 percentmaximum manganese, 1.0 percent maximum silicon, 0.35 percent maximumaluminum, 0.030 percent maximum sulfur, 0.001-0.01 percent boron,balance iron; and Alloy 718, having a nominal composition in weightpercent of from about 50 to about 55 percent nickel, from about 17 toabout 21 percent chromium, from about 4.75 to about 5.50 percentcolumbium plus tantalum, from about 2.8 to about 3.3 percent molybdenum,from about 0.65 to about 1.15 percent titanium, from about 0.20 to about0.80 percent aluminum, 1.0 percent maximum cobalt, and balance irontotaling 100 percent by weight.

Optionally, nonmetallic powders may be mixed with the metallic powders.The nonmetallic powders are typically hard intermetallic compounds suchas carbides, borides, or the like that are not melted during welding butare incorporated into the weldment when the weld rod is later used in awelding procedure.

The metallic powders (and nonmetallic powders, if any) are mixed with athermoplastic binder to form an injection-moldable mixture, step 22. Thethermoplastic binder is temporary in the sense that it is removed in alater step and is not present in the final weld rod. The thermoplasticbinder may be any operable thermoplastic binder suitable for sinteringoperations, preferably an organic or hydrocarbon thermoplastic binder.Examples include polyethylene, polypropylene, wax such as paraffin waxor carnuba wax, and polystyrene. A sufficient amount of thethermoplastic binder is used to render the mixture cohesive and pliableat temperatures above the thermoplastic temperature of the thermoplasticbinder. The mixing of the powders and the binder is preferably performedat a mixing temperature that is above the thermoplastic temperature ofthe thermoplastic binder, which is typically 200° F. or greater butdepends upon the specific thermoplastic binder material that is used.The thermoplastic binder material becomes flowable or “molten” at andabove the thermoplastic temperature, which aids in the mixing. Themixing at this mixing temperature achieves a mixture that is flowableand injection moldable at or above the thermoplastic temperature, butwhich is relatively inflexible and hard below the thermoplastictemperature.

The injection-moldable mixture preferably does not contain any addedwater, although there may be a minor amount of water present as animpurity. A substantial amount of water, if present, would chemicallyreact with the constituents of typical alloys of interest. The presenceof a significant amount of water may also lead to centerline porosityafter injection molding and sintering. Centerline porosity, if present,may be removed by swaging or a similar mechanical deformation processwhere the alloy is malleable. However, the removal of the centerlineporosity adds to the cost of the product, a cost that is avoided in thepresent approach. Additionally, such gross mechanical deformationprocesses cannot be readily used with many alloys that may be made intofiller-metal weld rods by the present approach due to their limitedductilities, such as intermetallic alloys and high-gamma-primenickel-base superalloys. Hot isostatic pressing cannot generally be usedto close internal porosity. Consequently, approaches that producecenterline porosity cannot be used to produce weld rods of many of thematerials of most interest. The combination of little or no water, useof thermoplastic binder, and elevated-temperature injection molding ofthe present approach aids in avoiding the centerline porosity, and nonehas been observed in prototype specimens of weld rod produced by thepresent approach. Accordingly, it is preferred that the thermoplasticbinder is non-aqueous, water is not mixed with the injection-moldablemixture, and no water is used in the subsequent step of removal ofexcess thermoplastic binder.

The injection-moldable mixture of metallic powders and thermoplasticbinder is thereafter injection molded to form an injection-molded rod,step 24. The injection molding step 24 is performed with theinjection-moldable mixture at an injection-molding temperature above thethermoplastic temperature of the thermoplastic binder. The thermoplasticbinder is therefore flowable, reducing the friction with the injectionnozzle during the injection molding. Any type of operableinjection-molding apparatus may be used to accomplish step 24. Apreferred injection-molding apparatus 40 is illustrated in FIG. 2. Theinjection-molding apparatus 40 includes an injection head 42 in the formof a chamber, with an injection nozzle 44 as the outlet of the chamber.A movable piston 46 forces the injection-moldable mixture 48 containedwithin the injection head 42 through the injection nozzle 44. Theinjection head 42 includes a controllable heater 49 that heats theinjection-moldable mixture to the injection-molding temperature. Theinjection nozzle 44 preferably has a circular cross section, although itcould have other shapes.

Preferably, no closed mold is used to receive and shape theinjection-moldable mixture 48 as it flows from the injection nozzle 44.Because of the rod shape of the weld rod that is being made, such aclosed mold would have to be elongated. It would be difficult toinjection mold into such an elongated hollow mold due to friction.Instead, a movable receiver 50 is positioned to receive theinjection-moldable mixture 48 that flows from the injection nozzle 44. Areceiving surface 52 of the movable receiver 48 moves away from theinjection nozzle 44 at a linear rate that is adjusted to be the same asthe linear rate at which the injection-moldable mixture 48 flows fromthe injection nozzle 44. This movement allows the injection-moldablemixture 48 to be smoothly and continuously deposited onto the movingreceiving surface 52. The shape of the injection-moldable mixture 48 ismaintained by the combination of this movement and the consistency ofthe mixture of the metal powders and the thermoplastic binder. In FIG.2, the movable receiver 50 is depicted as a continuous conveyer, but itcould be any other operable structure such as a movable plate-likesurface.

To perform the injection molding step 24 using this preferredinjection-molding apparatus 40, the injection-moldable mixture 48 isloaded into the injection head 42. The piston 46 is moved to force theinjection-moldable 48 mixture out of the injection nozzle 44 and ontothe movable receiver 50. The receiving surface 52 of the movablereceiver 50 moves away from the injection nozzle 44 at the same linearrate as the injection-moldable mixture 48 is forced from the injectionnozzle 44, so that the injection-molded mixture is deposited upon thereceiving surface 52 to form an injection molded rod 54. Theinjection-moldable mixture 48 is above the thermoplastic temperature ofthe thermoplastic binder as it emerges from the injection nozzle 44. Theinjection-moldable mixture quickly cools so that by a point about 2inches or so from the injection nozzle 44 the injection-moldable mixture48 is below the thermoplastic temperature of the thermoplastic materialand is therefore relatively rigid and hard. It may therefore be pickedup and handled with care.

Any excess thermoplastic binder is thereafter removed from an externalsurface 56 of the injection-molded rod 54, step 26. The excessthermoplastic binder is readily removed with a solvent for the excessthermoplastic binder. The solvent is contacted to the external surface56 to dissolve the excess thermoplastic binder at the surface of theinjection-molded rod 54 and below the surface as well. The solvent isselected according to the specific thermoplastic binder that is used.The solvent is preferably not aqueous in nature.

The injection-molded rod 54 is thereafter sintered, step 28, at asintering temperature to form a filler-metal weld rod 58, illustrated inFIG. 3. The sintering is preferably performed in a vacuum oven. As thetemperature of the injection-molded rod 54 is increased, the remainingtemporary thermoplastic binder is evaporated and removed, preferablyleaving no trace chemicals that might later contaminate the weld. Thesintering is preferably solid-state sintering and thus below the meltingpoint of the metal. After sintering, the filler-metal weld rod 58preferably has a cylindrical diameter of from 0.010 inch to 0.250 inch,preferably 0.035 to 0.070 inch. The diameter of the injection-molded rod54 is therefore somewhat greater than this sintered cylindrical diameterof the filler-metal weld rod 58, to account for shrinkage duringsintering. The filler-metal weld rod 58 may be of a selected shortlength or of a much longer length for use in automated weldingapparatus.

The sintering step 28 preferably sinters the filler-metal weld rod 58 toa relative density of not greater than 90 percent. The “relativedensity” is the percentage of the full density that is reached. Forexample, the weight of a weld rod 58 of 90 percent relative density is90 percent of the weight of a weld rod of the same volume and samematerial, but of full density. Preliminary studies have demonstratedthat a relative density of 90 percent or slightly lower is sufficientfor the weld rod 58 to perform as required in subsequent weldingoperations.

On the other hand, for some other welding operations the filler-metalweld rod 58 must have a higher relative density in order to performsuccessfully. The higher relative density is preferably not achievedwith further sintering, because the sintering times and temperaturesbecome prohibitively large. Instead, to achieve a higher relativedensity the filler-metal weld rod is preferably optionally furtherdensified by a process such as hot isostatic pressing, step 30. Hotisostatic pressing at a temperature of greater than about 2100° F. fornickel-base superalloys or greater than about 2150° F. for titaniumaluminides, at a pressure of from about 15,000 to about 25,000 poundsper square inch, and for a time of about 1-5 hours increases therelative density of the weld rod 58 to about 98-99 percent.

Initial studies indicate that the as-fabricated weld rod 58 issufficiently straight, of round cross section, and of the desireddiameter to be used for most applications. Centerless grinding, step 32,may optionally be used to improve the quality of the surface finish ofthe weld rod 58, if desired.

The final filler-metal weld rod 58 is used in a welding procedure, step34. The welding may be surface welding of a single article. Such weldingis used, for example, to repair a damaged region at the surface of thearticle, and for this application the composition of the filler metal istypically the same as that of the substrate being repaired. Surfacewelding may also be used to apply a coating, such as a hard facing, tothe surface of the article. The filler-metal weld rod 58 may also beused to join two or more pieces together by welding.

The present approach has been reduced to practice to make 0.050 inchdiameter weld rod of Rene™ 142 alloy, in pieces about 24 inches inlength, both with and without steps 30 and 32 of FIG. 1. There were nocenterline defects.

Although a particular embodiment of the invention has been described indetail for purposes of illustration, various modifications andenhancements may be made without departing from the spirit and scope ofthe invention. Accordingly, the invention is not to be limited except asby the appended claims.

1. A method for preparing a filler-metal weld rod of a filler-metalcomposition, comprising the steps of providing a mass of metallicpowders, wherein the mass of metallic powders together have thefiller-metal composition; mixing the metallic powders with a temporarythermoplastic binder to form an injection-moldable mixture; thereafterinjection molding the injection-moldable mixture at an injection-moldingtemperature above the thermoplastic temperature of the thermoplasticbinder to form an injection-molded rod; thereafter removing excessthermoplastic binder from an external surface of the injection-moldedrod; and thereafter sintering the injection-molded rod to form thefiller-metal weld rod, wherein the temporary thermoplastic binder isremoved in the step of sintering.
 2. The method of claim 1, wherein thestep of providing the mass of metallic powders includes the step ofproviding the metallic powders that are all of substantially the samecomposition.
 3. The method of claim 1, wherein the step of providing themass of metallic powders Includes the step of providing the net metalliccomposition as a nickel-base superalloy.
 4. The method of claim 1,wherein the step of providing the mass of metallic powders Includes thestep of providing the net metallic composition as a nickel-basesuperalloy that Is heat treatable to produce more than about 30 volumepercent gamma prime phase.
 5. The method of claim 1, wherein the step ofproviding includes the step of providing the mass of metallic powdershaving a nominal filler-metal composition in weight percent of about12.0 percent cobalt, about 6.8 percent chromium, about 1.5 percentmolybdenum, about 4.9 percent tungsten, about 2.8 percent rhenium, about6.35 percent tantalum, about 6.15 percent aluminum, about 1.5 percenthafnium, about 0.12 percent carbon, about 0.015 percent boron, balancenickel and minor elements.
 6. The method of claim 1, wherein the step ofproviding includes the step of providing the mass of metallic powdershaving a nominal filler-metal composition in weight percent of fromabout 7.4 to about 7.8 percent chromium, from about 5.3 to about 5.6percent tantalum, from about 2.9 to about 3.3 percent cobalt, from about7.6 to about 8.0 percent aluminum, from about 0.12 to about 0.18 percenthafnium, from about 0.5 to about 0.6 percent silicon, from about 3.7 toabout 4.0 percent tungsten, from about 1.5 to about 1.8 percent rhenium,from about 0.01 to about 0.03 percent carbon, from about 0.01 to about0.02 percent boron, balance nickel and incidental impurities.
 7. Themethod of claim 1, wherein the step of providing the mass of metallicpowders includes the step of providing the net metallic composition asan intermetallic alloy.
 8. The method of claim 1, wherein the step ofproviding the mass of metallic powders includes the step of providingthe net metallic composition as a titanium aluminide intermetallicalloy.
 9. The method of claim 1, wherein the step of providing Includesthe step of providing the mass of metallic powders having a nominalfiller metal composition in atomic percent of from about 45.5 to about48.0 percent aluminum and from about 48 to about 50.5 percent titanium,with the balance other elements.
 10. The method of claim 1, wherein thestep of providing includes the step of providing nonmetallic particlesmixed with the metallic powders.
 11. The method of claim 1, wherein thestep of mixing includes the step of mixing the metallic powders and thetemporary thermoplastic binder at a mixing temperature above thethermoplastic temperature of the thermoplastic binder.
 12. The method ofclaim 1, wherein the step of sintering includes the step of preparingthe filler-metal weld rod having a cylindrical diameter of from 0.010 to0.250 inch.
 13. The method of claim 1, wherein the step of sinteringincludes the step of sintering the filler-metal weld rod to a relativedensity of not greater than 90 percent.
 14. The method of claim 1,including an additional step, after the step of sintering, of hotisostatic pressing the filler-metal weld rod.
 15. The method of claim 1,including an additional step, after the step of sintering of centerlessgrinding the filler-metal weld rod.
 16. The method of claim 1, whereinthe step of injection molding includes the steps of providing aninjection-molding apparatus including an injection head with aninjection nozzle, and a movable receiver positioned to receive theInjection-moldable mixture flowing from the injection nozzle, loadingthe injection-moldable mixture into the injection head, and forcing theinjection-moldable mixture out of the injection nozzle onto the movablereceiver, while moving the movable receiver away from the injectionnozzle at the same linear rate as the injection-moldable mixture isforced from the Injection nozzle.
 17. A method for preparing afiller-metal weld rod of a filler-metal composition, comprising thesteps of providing a mass of metallic powders, wherein the metallicpowders are all substantially of the filler-metal composition andwherein the filler-metal composition is a titanium aluminide or anickel-base superalloy that is heat treatable to produce more than about30 volume percent gamma prime phase; mixing the metallic powders with atemporary thermoplastic binder to form an injection-moldable mixturewithout adding any water; thereafter injection molding theinjection-moldable mixture at an injection-molding temperature above thethermoplastic temperature of the thermoplastic binder to form aninjection-molded rod; thereafter removing excess thermoplastic binderfrom an external surface of the injection-molded rod using a non-aqueoussolvent; and thereafter sintering the injection-molded rod to form thefiller-metal weld rod, wherein the temporary thermoplastic binder isremoved in the step of sintering.
 18. The method of claim 17, whereinthe step of providing includes the step of providing nonmetallicparticles mixed with the metallic powders.
 19. The method of claim 17,wherein the step of sintering includes the step of preparing thefiller-metal weld rod having a cylindrical diameter of from 0.010 to0.250 inch.
 20. The method of claim 17, wherein the step of sinteringincludes the step of sintering the filler-metal weld rod to a relativedensity of not greater than 90 percent,
 21. The method of claim 17,including an additional step, after the step of sintering, of hotisostatic pressing the filler-metal weld rod.
 22. The method of claim17, including an additional step, after the step of sintering, ofcenterless grinding the filler-metal weld rod.
 23. The method of claim17, wherein the step of Injection molding includes the steps ofproviding an injection-molding apparatus including an injection headwith an injection nozzle, and a movable receiver positioned to receivethe injection-moldable mixture flowing from the injection nozzle,loading the injection-moldable mixture into the injection head, andforcing the injection-moldable mixture out of the injection nozzle ontothe movable receiver, while moving the movable receiver away from theinjection nozzle at the same linear rate as the injection-moldablemixture is forced from the injection nozzle.
 24. The method of claim 1,wherein the step of mixing includes the step of mixing the metallicpowders with a temporary thermoplastic binder to form aninjection-moldable mixture, without adding any water,
 25. The method ofclaim 1, wherein the step of removing includes the step of removingexcess thermoplastic binder from an external surface of theinjection-molded rod using a nonaqueous solvent.